Studies indicate a beneficial effect of protein reduction on progressive renal disease in rodents. Results in other species are variable. The program seeks to test in non-human primate the proposal that relative excess of protein intake may be responsible for a glomerulopathy and progressive loss of GFR in chronic renal insufficiency and that a reduced protein diet may be protective. The investigation was initiated in 1986 in monkeys (Papio hamadryas) with 5/8 reduction in renal mass. Two groups of 7 animals fed either an 8% or a 25% protein diet are compared. The diets are isocaloric and equal in fat, sodium, phosphorus, calcium, oligoelements and vitamins. Dietary intake is assessed from sodium, potassium and urea nitrogen excretion. Serial studies compare hemodynamic and metabolic data at 4 month intervals in awake animals a) Renal clearances: clearances of inulin are significantly higher after 5 years in 25% than in 8% protein fed monkeys; they do, however, decrease faster in time with high than with low protein diet; b) 24 hr urinary protein excretion: so far, proteinuria is minimal and not different between the 2 groups; c) Systemic arterial blood pressure: both groups are equally hypertensive with an increase of about 20mmHg in mean arterial pressure; d). Finally, in 1995, all 14 remnant and 4 uninephrectomized "control" monkeys will be euthanatized and necropsied. The morphology and ultrastructure of the viable portion of the remnant kidney will be examined by light and electronmicroscopy, and compared with each animal's intact kidney removed at the beginning of the study and with renal biopsies obtained during the study. Histopathologic changes of superfical glomeruli were minimal and equivalent in both groups at 40 months of follow-up Ancillary studies address differences between the 2 groups in peripheral renin activity, lipid profile, glomerular permselectivity, 17 (OH) corticosteroid excretion, parathyroid hormone muscle catabolism and bone histology. The results of this study will complement those of the ongoing NIH Modification of Diet in Renal Disease Study.